Suxamethonium-induced facilitation of spontaneous frontal EMG activity

The behaviour of spontaneous frontal electromyographic activity (FEMG) was studied during the recovery from suxamethonium and vecuronium block. In order to obtain comparable conditions in the study groups, the duration of the suxamethonium block was prolonged with a suxamethonium infusion. The FEMG was continuously recorded and the evoked electromyographic (EEMG) and twitch tension (ETT) responses were measured every 10 s from the thenar muscles. The median FEMG remained at the base level in 8 of the 12 vecuronium patients, despite a 50% recovery of EEMG. In the suxamethonium group there was an increase in FEMG in all six patients when EEMG had recovered to 10%, and significantly higher FEMG readings were obtained during further recovery from the block. Thus, early recovery of neuromuscular transmission is detected by FEMG more easily when suxamethonium is used instead of vecuronium. The different behaviour of FEMG may reflect a difference in the recovery ratio of ETT/EEMG or in the anaesthetic depth caused by the two types of neuromuscular blockers.